1. E. Meissner, Proc. Int. Congress Appl. Mech. (Z�rich, 1926) p. 3.
2. T. Matuzawa, Bull. Earth Res. Inst. (Tokyo)6 (1929), 225.
3. Y. Sato, Bull. Earth Res. Inst. (Tokyo)30 (1952), 1.
4. R. Stoneley, Mont. Not. Roy. Astron. Soc., Geophys. Suppl.5 (1949), 222.
5. N. Ricker, Proc. Third World Petrol Cong., Sect. 1 (1951), p. 514.